55636.20091009 Occultation October 09, 2009

(last updated 2009 10 08)

Across the globe pictured above, the three solid lines correspond to the northern limit, centerline, and southern limit of 55636's shadow. The northern and southern limits correspond to a radius of 405 km (using an assumed albedo of 0.1). The upper and lower dashed lines indicate the effects of unknown systematic errors such as catalog zone errors. Previous KBO appulse analyses have shown the observed error to be 1.5-2 times that of the prediction's random error. The shaded area represents where the sun is more than 12 degrees below the horizon.

The scientific goals of this event are (i) to accurately determine the diameter of 55636, (ii) to probe for a tenuous atmosphere of 55636, and (iii) to detect possible nearby satellites of 55636.

Observations are worthwhile and encouraged from any location at which the event is visible. Due to the possibilities of the occultation star being a multiple star system or the KBO having a satellite; either of these could move the event by more than the systematic effect uncertainties shown.

Table 1: Prediction Details

Geocentric Mid-time (yyyy month dd hh:mm:ss)

2009 October 09 10:30:07± 00:00:081 UT

Minimum Geocentric Separation

0.0593± 0.00631 arcsec

Position Angle (55636 relative to the star; measured north through east)

Table 3: Projected KBO Offsets from Reference Ephemeris at the Time of the Event

Body

RA (arcsec)

Dec (arcsec)

55636

+0.2654± 0.0075

–0.073± 0.006

See Notes 5 and 6

3Measured position corresponds to RA offset of +0.1341'' and Dec. offset of +0.041''.

4All "offsets" are defined in the ("corrected" – "reference") or ("observed" – "calculated") sense. The offsets should be added to reference positions to get the measured positions, which we use to calculate the prediction.

4Data analyzed using UCAC2 reference network. A weighted average of the data from the two telescopes was used to calculate the RA and DEC. The errors given are 1 standard deviation.

6Data from the SMARTS 0.9m (35 frames) , USNO 40-inch (7 frames), and USNO 61-inch (28 frames) telescopes over the span of 3 years were reduced with respect to stars in the UCAC2 catalog. A model was developed to fit the residuals obtained from our measured positions compared to that of the object's JPL ephemeris. All residuals obtained from the different telescopes were consistent with the model. The model includes the first-order effects of errors in the orbital elements of 55636: (i) constant offsets in RA and Dec, (ii) linear (in time) offsets in RA and Dec, and (iii) sinusoidal terms with the Earth's orbital period. The model was propagated to obtain the predicted position and error of the KBO at the time of the occultation. The errors listed for the KBO are 1 standard deviation.

Discussion

On 2009 October 9th, 55636 (2002 TX300) will occult will occult 2UCAC number 41650964. The above map and the following prediction results are from the analysis of 59 frames obtained using the United States Naval Observatory 61-inch and 40-inch telescopes taken by Stephen Levine and Trudy Tilleman, and the SMARTS 0.9m telescope taken by Joselino Vasquez. The 70 frames, taken between August 2007 and September 2009, were used to develop an ephemeris correction model to fit the residuals from our measured positions compared to that of the object's JPL ephemeris. The model includes the first-order effects of errors in the orbital elements of 55636: (i) constant offsets in RA and Dec, (ii) linear (in time) offsets in RA and Dec, and (iii) sinusoidal terms with the Earth's orbital period. With this approach, the error in the JPL ephemeris does not enter into our prediction error, since the ephemeris is used only as a reference ephemeris for our correction model.

For the occultation star, 69 frames obatined using the United States Naval Observatory 61-inch and 40-inch taken by Stephen Levine and Trudy Tilleman were used to calculate the RA and Dec position.

The sites in the table below are listed in order of their distance from the predicted centerline, starting with the most northern site.

Site

East Longitude

Latitude

Site Altitude6

(km)

Distance7

(km)

Velocity

(km/s)

Behlen Observatory (Nebraska U.)

–96 26 48

41 10 18

0.362

2812 N.

25.47

Fickle Hill Observatory

–123 59 09

40 48 08

0.61

2407

25.49

Puckett Observatory

–84 55 00

33 45 00

0.30

2381 N.

25.42

Lick Obs.

–121 38 12

37 20 36

1.29

2032 N.

25.58

Fremont Peak

–121 29 55

36 45 36

0.84

1968 N.

25.59

USNO

–111 44 24

35 11 00

2.31

1881 N.

25.55

M.R.O.

–107 11 05

33 58 36

2.22

1818 N.

25.54

Pomona College

–117 42 35

34 05 51

0.35

1698 N.

25.58

Puerto Rico (Arecibo)

–66 45 12

18 20 36

0.50

1643 N.

25.31

Mt. Graham (VTT)

–109 53 21

32 42 04

3.19

1635 N.

25.56

Palomar

–116 51 54

33 21 24

1.71

1623 N.

25.58

Arizona Sky Village (David Churchill)

–109 07 33

31 56 49

1.4

1565 N.

25.55

Arizona Sky Village (Jack Newton)

–109 07 08

31 55 30

1.4

1562 N.

25.55

McDonald Observatory (Mt. Locke)

–104 01 21

30 40 17

2.08

1520 N.

25.53

Guillermo Haro Obs.

–110 23 05

31 03 10

2.480

1447 N.

25.58

San Pedro Martir, Mexico

–115 27 49

31 02 39

2.83

1382 N.

25.58

Brownsville, Texas

–97 29 22

25 56 47

0.121

1171 N.

25.51

Leeward Community College

–157 59 04

21 23 28

0.02

743 N.

25.70

Windward Community College

–157 48 54

21 24 36

0.06

740 N.

25.70

Haleakala

–156 15 24

20 42 24

3.05

620 N.

25.70

IRTF

–155 28 29

19 49 46

4.18

506 N.

25.70

Mauna Kea Mid-Level

–155 27 15

19 45 36

2.8

499 N.

25.70

Tonantzintla Observatory

–98 18 50

19 01 58

2.2

420 N.

25.52

Acapulco

–99 53 16

16 51 33

0.0

152 N.

25.54

Obs. Ast. de la UNAN - Managua (Nicaragua)

–86 16 14

12 06 25

0.25

127 N.

25.69

Cairns, Australia

145 46 28

–16 55 25

0.08

1 N.

25.50

Townesville

146 45 00

–19 15 00

0.0

254 S.

25.24

Black Springs

138 53 18

–33 53 58

0.47

994 S.

25.43

Toowoomba

151 57 00

–27 34 12

0.69

1218 S.

25.51

Siding Spring

149 03 44

–31 16 17

1.21

1337 S.

25.49

Grove Creek Obs. (Sydney)

149 21 59

–33 49 46

0.90

1538 S.

25.48

Mount Stromlo

149 03 44

–35 18 57

0.81

1624 S.

25.48

Hobart

147 26 24

–42 48 18

0.04

2042 S.

25.45

Auckland

174 46 42

–36 54 24

0.80

2943 S.

25.59

Mt. John

170 27 50

–43 59 22

1.04

3108 S.

25.54

Geocenter

----------

---------

center of Earth

1758 S.

25.29

6Altitude of each observatory is measured in kilometers above sea level.

7"Distance" refers to the closest approach distance of the "Site" to the center of 55636's shadow in the shadow plane. The errors on all closest approach distances are ±184 km (one standard deviation). "S." means the site is south of the center of 55636's shadow. "N." means the site is north of the center of 55636's shadow.

Table 5: 55636.20091009 Occultation Predictions for Individual Sites

Site

55636 Immersion (UT)9

UT Mid-Time

KBO Altitude

Solar Altitude9

55636 Emersion (UT)9

Acapulco

10:26:21

10:26:36

27°

-----------

10:26:51

Arizona Sky Village (Jack Newton)

-----------

10:26:58

41°

-----------

-----------

Arizona Sky Village (David Churchill)

-----------

10:26:58

41°

-----------

-----------

Auckland

-----------

10:32:25

24°

-----------

-----------

Behlen Observatory (Nebraska U.)

-----------

10:26:40

33°

-----------

-----------

Black Springs

-----------

10:33:50

11°

-----------

-----------

Brownsville, Texas

-----------

10:26:30

30°

-----------

-----------

Cairns, Australia

10:33:27

10:33:42

27°

-----------

10:33:58

Fickle Hill Observatory

-----------

10:27:40

52°

-----------

-----------

Fremont Peak

-----------

10:27:32

51°

-----------

-----------

Guillermo Haro Obs.

-----------

10:27:01

42°

-----------

-----------

Grove Creek Obs. (Sydney)

-----------

10:33:31

17°

-----------

-----------

Haleakala

-----------

10:29:40

78°

-----------

-----------

Hobart

-----------

10:33:25

9°

-----------

-----------

Leeward Community College

-----------

10:29:40

78°

-----------

-----------

Lick Obs.

-----------

10:27:33

51°

-----------

-----------

M.R.O.

-----------

10:26:55

40°

-----------

-----------

IRTF

-----------

10:29:38

76°

-----------

-----------

Mauna Kea Mid-Level

-----------

10:29:38

76°

-----------

-----------

McDonald Observatory (Mt. Locke)

-----------

10:26:46

37°

-----------

-----------

Mt. Graham (VTT)

-----------

10:27:00

41°

-----------

-----------

Mt. John

-----------

10:32:35

17°

-----------

-----------

Mt. Stromlo

-----------

10:33:30

15°

-----------

-----------

Obs. Ast. de la UNAN - Managua (Nicaragua)

10:25:57

10:26:12

15°

-16°

10:26:27

Palomar

-----------

10:27:19

46°

-----------

-----------

Pomona College

-----------

10:27:21

48°

-----------

-----------

Puckett Observatory

-----------

10:26:15

21°

-15°

-----------

Puerto Rico (Arecibo)

-----------

10:25:54

21°

2°

-----------

San Pedro Martir, Mexico

-----------

10:27:14

46°

-----------

-----------

Siding Spring

-----------

10:33:33

18°

-----------

-----------

Tonantzintla Observatory

-----------

10:26:32

28°

-----------

-----------

Toowoomba

-----------

10:33:28

23°

-----------

-----------

Townsville

10:33:28

10:33:41

25°

-----------

10:33:53

USNO

-----------

10:27:06

42°

-----------

-----------

Windward Community College

-----------

10:29:45

78°

-----------

-----------

Geocentric

-----------

10:30:07

-----------

-----------

9The errors on all times are ±0:08 (8 seconds; one standard deviation). The solar altitude is given for locations where it is relevant (solar altitude greater than -18°). No entry in the immersion and emersion columns indicates that the occultation is not predicted to be visible at that site. But due to unknown effects (stellar or KBO duplicity), some of these sites may see an occultation event that would be centered on the time in the "UT Mid-Time" column.